1. Field of the Invention
This invention relates to a millimeter-wave focal plane array and, in particular, to apparatus, systems and methods for a dual-band focal plane array with simultaneous response at infrared and millimeter-wave frequency bands.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Conventional millimeter-wave focal plane array pixel spacing is limited by the wavelength of the millimeter wave (mmW), typically having a wavelength of approximately 3 mm which corresponds to a frequency of approximately 100 GHz. As shown in FIG. 1, the system 10 includes an optical lens 12 that focuses millimeter-wave radiation within the field of view into an array of pixel elements 20 positioned in the focal plane 15 of the lens 12. Millimeter radiation from a scene within the field of view is directed onto the focal plane array 20 by optical lens 12 or other millimeter wave device. The pixel spacing on the focal plane array is approximately one wavelength between sensors because the spatial resolution spot produced by the optical lens 12 onto the focal plane array 20 is proportional to the wavelength. Therefore, a focal plane array tuned for long-wavelength radiation would have pixels spaced by a larger distance than would a focal plane array tuned for a shorter wavelength radiation.
Antenna-coupled metal-oxide-metal (MOM) diodes was used in the past for detection and mixing in the infrared (IR) and millimeter-wave (mmW) portion of the spectrum as described in Boreman et al, “Antenna-coupled metal-oxide-metal diodes for dual band detection at 92.5 GHz and 28 THz”, Electronics Letters, Vol. 40, No. 2, Jan. 22, 2004. The ratio between the two required frequencies of operation is approximately 300:1. One example of a design using the antenna-coupled MOM diode includes a frequency dependent antenna structure with a small enough feed to allow for operation at the higher frequency limit with the diode located at the antenna feed. In another example, the diode is integrated with two resonant antenna structures at the two required frequencies of operation.
The MOM diode is located at the center of the slot antenna and is connected to an infrared antenna to achieve infrared and millimeter wave responses. The responses are improved by matching the impedance of the diode and the antennas. The infrared response can be further improved by decreasing the junction, which decreases the junction capacitance and therefore increases the cutoff frequency of the diode.
Therefore, a need exists for a dual-band focal plane array with two different spatial resolutions, one for long-wavelength radiation, and one for short-wavelength radiation.